1. Field of the Invention
The present invention relates to flowmeters suitably used for measuring the flow rate of a fluid in fluid transport pipes in various industrial fields, such as chemical factories, semiconductor manufacturing, food manufacturing, and biotechnology, and to flow-rate controllers equipped with such flowmeters.
This application is based on Japanese Patent Application No. 2009-024713, the content of which is incorporated herein by reference.
2. Description of Related Art
In the related art, various kinds of flowmeters for measuring the flow rate of a fluid have been proposed. One example is a differential-pressure flowmeter that is advantageous when, for example, measuring the flow velocity of a liquid since the flowmeter can accurately measure a flow rate with the occurrence of fewer measurement errors, as compared with a laser flowmeter or the like that is susceptible to the effect of air bubbles included in a fluid. Therefore, various flow-rate controllers using differential-pressure flowmeters have been proposed (for example, see Japanese Unexamined Patent Application, Publication No. 2007-34667).
However, a differential-pressure flowmeter has a problem in that the measurable flow-rate range thereof is limited, as compared with flowmeters of other types. Specifically, the problem is that the upper limit of the measurable flow-rate range is limited to a flow rate that is about ten times the flow rate at the lower limit.
Therefore, one conceivable method of measuring the flow rate of a fluid in a range exceeding the measurable flow-rate range in a differential-pressure flowmeter is using a combination of multiple differential-pressure flowmeters.
However, this is problematic in that the cost of manufacture of the flowmeter or the flow-rate controller increases due to an increase in the number of flowmeters to be used for measuring the flow rate.